Using the pinky

Hey Mike,
I'm a new user of this site.I just wanted to know if it is necessary to use my pinky on my left hand(I'm right handed).
I can achieve great speed with three fingers.Is it bad technique to use three?

The general rule is one finger per fret, but some people don't incorporate the pinky of their fretting hand

Famous examples - Flea said in an interview once that he doesn't use his pinky; he might of changed since the time of the interview. I believe Rocco Prestia actually uses two fingers for fretting and the other two are for muting.

Not-so Famous Exmaples - My friend, who plays guitar, used to do that, but learned to use all four when trying to learn the riff to Crazy Train.

I used to have a bad habit of not using the pinkey on my left hand but since I've taken lessons, man, it helps a ton. I pretty much use the one finger per fret and my speed has increased a lot for slapping. I agree with abark000 that using the pinkey will definitley help out.